Denitrification by Anaeromyxobacter dehalogenans, a Common Soil Bacterium Lacking the Nitrite Reductase Genes nirS and nirK

The versatile soil bacterium lacks the hallmark denitrification genes and (encoding NO →NO reductases) and couples growth to NO reduction to NH (respiratory ammonification) and to N O reduction to N also grows by reducing Fe(III) to Fe(II), which chemically reacts with NO to form N O (i.e., chemodenitrification). Following the addition of 100 μmol of NO or NO to Fe(III)-grown axenic cultures of , 54 (±7) μmol and 113 (±2) μmol N O-N, respectively, were produced and subsequently consumed. The conversion of NO to N in the presence of Fe(II) through linked biotic-abiotic reactions represents an unrecognized ecophysiology of The new findings demonstrate that the assessment of gene content alone is insufficient to predict microbial denitrification potential and N loss (i.e., the formation of gaseous N products). A survey of complete bacterial genomes in the NCBI Reference Sequence database coupled with available physiological information revealed that organisms lacking or but with Fe(III) reduction potential and genes for NO and N O reduction are not rare, indicating that NO reduction to N through linked biotic-abiotic reactions is not limited to Considering the ubiquity of iron in soils and sediments and the broad distribution of dissimilatory Fe(III) and NO reducers, denitrification independent of NO-forming NO reductases (through combined biotic-abiotic reactions) may have substantial contributions to N loss and N O flux. Current attempts to gauge N loss from soils rely on the quantitative measurement of and genes and/or transcripts. In the presence of iron, the common soil bacterium is capable of denitrification and the production of N without the key denitrification genes and Such chemodenitrifiers denitrify through combined biotic and abiotic reactions and have potentially large contributions to N loss to the atmosphere and fill a heretofore unrecognized ecological niche in soil ecosystems. The findings emphasize that the comprehensive understanding of N flux and the accurate assessment of denitrification potential can be achieved only when integrated studies of interlinked biogeochemical cycles are performed.